A battery

Abstract

The application provides a battery, in particular a lithium ion battery with high safety and high low-temperature performance, which comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; wherein the negative electrode active material in the negative electrode sheet is graphite, the value of Raman spectrum D / G of the graphite is 0.05-0.25; the electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent comprises a first solvent with a dielectric constant > 40; and the additive comprises a first additive containing a-S-O-C- bond. By optimizing the value of Raman spectrum D / G of the negative electrode active material and the composition of the electrolyte, a stable SEI film is constructed, so that the battery has better high-temperature and low-temperature performance. Meanwhile, by optimizing the composition of the electrolyte and the structure of the battery, the safety performance of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a battery that has superior high and low temperature performance while also possessing high safety. Background Technology

[0002] Due to their superior performance characteristics such as high operating voltage, high energy density, long cycle life, low self-discharge rate, and no memory effect, lithium-ion batteries have experienced rapid development in recent years. Simultaneously, the application scope of lithium-ion batteries continues to expand, from the information industry (mobile phones, PDAs, laptops, etc.) to energy and transportation (electric vehicles, grid peak shaving, solar energy, wind power station energy storage, etc.). High reliability and high safety have become fundamental requirements for lithium-ion batteries. With technological advancements, people have increasingly higher performance requirements for lithium-ion batteries, expecting them to possess excellent high and low temperature performance and good safety performance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a battery, particularly one with superior high and low temperature performance while also possessing high safety performance. The battery of this invention achieves this by optimizing the negative electrode active material (selecting an appropriate Raman spectral D / G value) and the electrolyte (selecting a first solvent with a dielectric constant >40 and a first additive containing -SOC- bonds) to construct a stable SEI film, reducing side reactions during charging and discharging and improving the battery's high and low temperature performance. Simultaneously, the battery's structural composition is optimized (selecting an aluminum-plastic film with a low-melting-point heat-sealing layer, and encapsulating it with low-melting-point tab adhesive) to obtain higher heat box pass rate and overcharge pass rate, significantly improving the battery's safety performance.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator; wherein the negative electrode active material in the negative electrode is graphite, and the Raman spectrum D / G value of the graphite is 0.05 to 0.25; the electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a first solvent with a dielectric constant > 40; and the additive comprises a first additive containing a -SOC- bond.

[0006] According to an embodiment of the present invention, the main function of the diaphragm is to separate the positive and negative electrode plates, prevent the two electrodes from contacting and causing a short circuit, and allow ions in the electrolyte to pass through.

[0007] According to an embodiment of the present invention, the positive electrode sheet includes a positive electrode active material, which is selected from at least one of lithium cobalt oxide, nickel-cobalt-manganese-lithium ternary materials, lithium iron phosphate, and lithium manganese oxide.

[0008] According to an embodiment of the present invention, the D / G value of the Raman spectrum of the graphite refers to the ratio of the peak intensities of the D peak to the G peak in the Raman spectrum of the graphite. In the Raman spectrum, the D peak appears at 1350 cm⁻¹. -1 The G peak appears at approximately 1580 cm. -1 The D / G ratio is the ratio of the D peak intensity to the G peak intensity. The Raman spectrum of the graphite was obtained using an Advantage 532 benchtop Raman spectrometer with a 532 light source, a sampling depth of 1.5–2 μm, and a scanning range of 0–3500 cm⁻¹. -1 .

[0009] According to an embodiment of the present invention, the graphite is graphite with amorphous carbon coated on its surface. The graphite can be prepared by methods known in the art, or obtained commercially.

[0010] According to an embodiment of the present invention, based on the total weight of the electrolyte, the content Y of the first solvent with a dielectric constant >40 is 20wt% to 40wt%, for example, 20wt%, 25wt%, 30wt%, 35wt%, or 40wt%.

[0011] According to an embodiment of the present invention, the first solvent with a dielectric constant >40 is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl sulfoxide, and sulfolane (SL). In this case, the electrolyte has high conductivity and can form a good SEI film.

[0012] Preferably, the first solvent with a dielectric constant >40 is selected from ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and optionally sulfolane (SL).

[0013] The content of the fluoroethylene carbonate (FEC) is 5wt% to 15wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%; the content of the sulfolane (SL) is 0wt% to 1wt%, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%.

[0014] The mass ratio of ethylene carbonate (EC) to propylene carbonate (PC) is 2:1 to 1:2.5, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1.2:1, 1.5:1 or 2:1.

[0015] According to an embodiment of the present invention, based on the total weight of the electrolyte, the content Z of the first additive containing -SOC- bonds is 2wt% to 5wt%, for example, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%.

[0016] According to embodiments of the present invention, the first additive containing a -SOC- bond is selected from at least one of 1,3-propanesulfonate lactone (PS), 1-propylene-1,3-sulfonate lactone (PST), ethylene sulfate (DTD), and butyrylamide lactone (BS). The first additive containing a -SOC- bond can form films at both the positive and negative electrodes. On the negative electrode surface, it forms a thinner and more stable SEI film composition, improving ionic conductivity. On the positive electrode surface, it forms a film that protects the positive electrode, inhibits metal ion dissolution, and reduces solvent reaction at the positive electrode.

[0017] According to embodiments of the present invention, the first additive containing a -SOC- bond is selected from 1,3-propanesulfonate lactone (PS), 1-propylene-1,3-sulfonate lactone (PST), ethylene sulfate (DTD), and butyrate lactone (BS), wherein the content of the 1,3-propanesulfonate lactone is 1 wt% to 4 wt% (e.g., 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%), and the content of the 1-propylene-1,3-sulfonate lactone is 0 wt% to 1 wt% (e.g., 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%). The butyryl lactone content is 0.5wt% to 2wt% (e.g., 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%), and the ethylene sulfate content is 0.5wt% to 1wt% (e.g., 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%). By further optimizing the composition of the first additive containing -SOC- bonds, the role of such additives can be better utilized, enabling the construction of more stable SEI and CEI films at the positive and negative electrodes, reducing side reactions in the electrolyte, stabilizing the structure of the cathode material, and significantly improving the high-temperature stability and low-temperature discharge capacity retention of the battery.

[0018] This invention selects anode active materials with a Raman spectral D / G value of 0.05–0.25. A smaller D / G value indicates higher graphite crystallinity, fewer surface defects in the anode active material, and fewer side reactions with the electrolyte. Based on this, a first solvent with a dielectric constant >40, possessing strong ion-separating ability and solvation capacity, is used to ensure high electrolyte conductivity and improve lithium-ion conduction rate. Simultaneously, the first solvent with a dielectric constant >40 can form an SEI film at the anode, improving the battery's discharge performance at low temperatures. Further, a first additive containing -SOC- bonds is added. This type of additive can form films at both the positive and negative electrodes. Constructing a stable SEI film at the anode effectively reduces electrolyte side reactions, while constructing a stable CEI film at the positive electrode stabilizes the cathode material structure, reduces impedance growth and metal ion dissolution during charging and discharging, and effectively improves the battery's high-temperature stability, especially float charging performance. The reduced impedance effectively improves the battery's low-temperature discharge capacity retention.

[0019] According to an embodiment of the present invention, the electrolyte further includes a second additive, the second additive being selected from one or more of the following compounds: vinylene carbonate, vinyl sulfate, butene sulfite, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0020] According to an embodiment of the present invention, the electrolyte further includes a second solvent, the second solvent being selected from at least one of linear carbonates and linear carboxylic esters.

[0021] According to an embodiment of the present invention, the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and the linear carboxylic acid ester is selected from at least one of ethyl propionate, propyl propionate, and propyl acetate.

[0022] According to an embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium difluoro(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium tri(trifluoromethylsulfonyl)methyl.

[0023] According to an embodiment of the present invention, the concentration of the lithium salt is 0.5 to 2.0 mol / L.

[0024] According to an embodiment of the present invention, the charging cutoff voltage of the battery is 4.45V or higher.

[0025] According to an embodiment of the present invention, the battery further includes tabs, the tabs include tab adhesive, and the melting point of the tab adhesive is 100°C to 160°C.

[0026] According to an embodiment of the present invention, the battery further includes an aluminum-plastic film, the aluminum-plastic film including a heat-sealing layer, the melting point of the heat-sealing layer being 100°C to 150°C.

[0027] Optimizing the electrolyte and battery structure can further improve battery safety performance. Specifically, the optimized electrolyte will generate a large amount of gas and heat inside the battery during hot box testing and overcharge testing. By selecting low-melting-point tab adhesive and low-melting-point encapsulation layer, flammable gases can be discharged in time before the battery thermal runaway, reducing the accumulation of heat inside the battery and improving the pass rate of the battery's hot box testing and overcharge testing.

[0028] The beneficial effects of this invention are:

[0029] This invention provides a battery, particularly a lithium-ion battery that exhibits superior high and low temperature performance while also possessing high safety. Specifically, a stable SEI film is constructed by optimizing the Raman spectrum D / G value of the negative electrode active material and the composition of the electrolyte, thereby enabling the battery to achieve superior high and low temperature performance. Simultaneously, the battery's safety performance is improved by optimizing the electrolyte and battery structure. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. Any modifications or equivalent substitutions to the technical solutions of the present invention that do not depart from the spirit and scope of the technical solutions of the present invention should be covered within the scope of protection of the present invention.

[0031] Lithium-ion battery manufacturing

[0032] (1) Preparation of positive electrode

[0033] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and acetylene black were mixed in a weight ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto a current collector aluminum foil. The coated aluminum foil was baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. Finally, the positive electrode sheet was obtained by rolling and slitting.

[0034] (2) Preparation of negative electrode

[0035] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, and conductive agent acetylene black were mixed in a weight ratio of 97:1:1:1. Deionized water was added, and the negative electrode slurry was obtained under the action of a vacuum stirrer. The negative electrode slurry was uniformly coated on high-strength carbon-coated copper foil, dried at room temperature, and then transferred to an 80°C oven for drying for 10 hours. After that, the negative electrode sheet was obtained by rolling and slitting.

[0036] (3) Electrolyte preparation

[0037] In a glove box filled with inert gas (argon) (H2O < 0.1 ppm, O2 < 0.1 ppm), a first solvent with a dielectric constant > 40 (specific selections are shown in Table 2), diethyl carbonate, and propyl propionate are mixed evenly, with the mass ratio of diethyl carbonate to propyl propionate being 2:5. Then, 1.25 mol / L of fully dried lithium hexafluorophosphate (LiPF6) and additives (specific selections are shown in Table 3) are quickly added and dissolved in the organic solvent. The mixture is stirred evenly, and after passing the tests for moisture and free acid, the electrolyte is obtained, as shown in Table 1.

[0038] (4) Preparation of lithium-ion batteries

[0039] The prepared positive electrode sheet (using tab adhesive with a melting point of 120℃), separator, and negative electrode sheet (using tab adhesive with a melting point of 120℃) are stacked in sequence, ensuring that the separator is positioned between the positive and negative electrodes to provide isolation. Then, the unfilled bare cell is obtained by winding. The bare cell is placed in an outer packaging foil (using an aluminum-plastic film with a heat-sealing layer with a melting point of 130℃), and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and sorting, the corresponding lithium-ion battery is obtained.

[0040] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0041] (1) 45℃ float charge test: The corresponding battery was adjusted to 50% SOC in a constant temperature environment of 25℃. The initial thickness T1 of the battery was tested when it arrived. The battery was placed in a constant temperature environment of 45℃ and charged to 4.45V with constant current and constant voltage at 0.5C. The constant voltage charging was carried out for 7 days as one cycle. The thermal thickness expansion change of the battery was monitored. The final thermal thickness T2 of the battery was tested under the condition that the battery was obviously bulging. The thickness expansion rate of lithium battery at 45℃ float charge = (T2-T1) / T1×100%. The results are shown in Table 4.

[0042] (2) -30℃ low temperature discharge test: The obtained batteries were placed in a constant temperature environment of 25℃. The batteries were discharged at 0.2C to 3.0V, charged at 0.7C constant current and constant voltage to 4.45V, and the cutoff current was 0.05C. After the batteries were fully charged, they were left to stand for 5 minutes, and then discharged at 0.5C constant current to the cutoff voltage of 3.0V. The battery discharge capacity at 25℃ and 0.5C was recorded as the initial capacity Q1. In a constant temperature environment of 25℃, the batteries were charged at 0.7C constant current and constant voltage to 4.45V, and the cutoff current was 0.05C to fully charge the batteries. Then the fully charged batteries were placed in a -30℃ environment and left to stand for 4 hours. When the surface temperature of the batteries reached the ambient temperature, they were discharged at 0.5C to 3.0V. The battery discharge capacity at -30℃ and 0.5C was recorded as Q2. The battery low temperature discharge capacity retention rate at -30℃ was calculated as Q2 / Q1×100%. The specific results are shown in Table 4.

[0043] (3) 130℃ hot box test: After the battery cell is fully charged by constant current and constant voltage at 0.5C, it is placed in a constant temperature chamber and heated by convection or circulating hot air chamber at an initial temperature of 20±5℃. The temperature of the hot box is increased to 130±2℃ at a rate of 5±2℃ per minute and maintained at this temperature for 30 minutes before the test ends.

[0044] Judgment criteria: The battery cell does not catch fire or explode within 30 minutes. Specific test results are shown in Table 4.

[0045] (4) 3C-5V overcharge test: Under the condition of ambient temperature (25±5)℃, the discharged cell is charged with constant current of 3C to 5.0V and then switched to constant voltage charging. The charging time is limited to 7 hours or the charging is stopped when the battery surface temperature is stable (temperature difference ≤2℃ within 45min).

[0046] Judgment criteria: The battery cell does not catch fire or explode. Specific test results are shown in Table 4.

[0047] Table 1. Composition of lithium-ion batteries in comparative and example cases.

[0048]

[0049] The combinations 1-1 to 1-7 in Table 1 represent first solvents with different compositions and contents and dielectric constants >40, as shown in Table 2:

[0050] Table 2. Composition of the first solvent with a dielectric constant > 40 and its percentage of the total electrolyte mass.

[0051] Combination 1-1 Combination 1-2 Combinations 1-3 Combinations 1-4 Combinations 1-5 Combinations 1-6 Combinations 1-7 EC / wt% 0 4 7.5 7 7 10 10 PC / wt% 0 4 7.5 7 7 14 15 FEC / wt% 0 2 5 10 15 15 20 SL / wt% 0 0 0 1 1 1 5 Total content / wt% 0 10 20 25 30 40 50

[0052] For example, combination 1-1 means that it does not contain a first solvent with a dielectric constant > 40; combination 1-4 means that the first solvent with a dielectric constant > 40 includes EC accounting for 7 wt% of the total mass of the electrolyte, PC accounting for 7 wt% of the total mass of the electrolyte, FEC accounting for 10 wt% of the total mass of the electrolyte, and SL accounting for 1 wt% of the total mass of the electrolyte.

[0053] The combinations 2-1 to 2-5 in Table 1 represent the first additives with different compositions and contents, as detailed in Table 3:

[0054] Table 3. Composition of the first additive and its percentage (wt%) in the total electrolyte.

[0055] Combination 2-1 Combination 2-2 Combination 2-3 Combinations 2-4 Combinations 2-5 PS / wt% 0 1 3 3 4 PST / wt% 0 0 0 0.5 0.5 DTD / wt% 0 0.5 0.5 0.5 0.5 BS / wt% 0 0.5 0.5 1 1 Total content / wt% 0 2 4 5 6

[0056] For example, combination 2-1 means that it does not contain the first additive; combination 2-3 means that the first additive includes 3 wt% PS, 0.5 wt% DTD, and 0.5 wt% BS.

[0057] Table 4. Electrical performance and safety test results of lithium-ion batteries in comparative and example cases.

[0058]

[0059] As shown in Table 4, Examples 1-5 show that as the D / G value of the negative electrode active material increases, the high-temperature performance of the battery gradually deteriorates, while the low-temperature discharge performance at -30℃ gradually improves. This is related to the coating on the graphite surface, where the coating of amorphous carbon on the graphite surface reduces polarization.

[0060] A comparison of Examples 2, 6, and 15 shows that when the first solvent and the first additive are outside the defined range, the battery performance is relatively poor; when they are within the defined range, the battery performance is optimal. This is mainly because when the content of the first solvent and the first additive is less than the defined range, the electrolyte conductivity is low, and the additive is insufficient, resulting in incomplete film formation and poor battery performance. When the content of the first solvent and the first additive is greater than the defined range, the higher viscosity of the electrolyte and the excessively thick film further degrade the battery performance.

[0061] Furthermore, batteries assembled with graphite having a D / Q value of 0.1 exhibit better high-temperature performance than those assembled with graphite having a D / Q value of 0.2. This is because, under high-temperature conditions, the side reactions between graphite with a D / Q value of 0.2 and the electrolyte are more intense due to the surface coating, compared to graphite with a D / Q value of 0.1. Conversely, the low-temperature performance is better; this is because the surface coating of graphite with a D / Q value of 0.2 results in less delithiation polarization and a higher low-temperature discharge capacity.

[0062] In summary, it can be seen that the lithium-ion battery using the solution of this invention possesses superior high and low temperature performance and high safety performance, demonstrating extremely high application value. The above is a detailed description of feasible embodiments of this invention, but it does not limit the scope of protection of this invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode, a negative electrode, an electrolyte, and a separator; wherein the negative electrode active material in the negative electrode is graphite, and the Raman spectrum D / G value of the graphite is 0.05~0.25; the electrolyte includes an organic solvent, a lithium salt, and additives, wherein the organic solvent includes a first solvent with a dielectric constant >40; and the additives include a first additive containing -SOC- bonds. The first solvent with a dielectric constant >40 is selected from ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and optionally sulfolane (SL); based on the total weight of the electrolyte, the content Y of the first solvent with a dielectric constant >40 is 20wt%~40wt%; The first additive containing a -SOC- bond is selected from 1,3-propanesulfonate lactone (PS), optionally 1-propene-1,3-sulfonate lactone (PST), ethylene sulfate (DTD), and butyrylamide lactone (BS); the content Z of the first additive containing a -SOC- bond is 2wt%~5wt% based on the total weight of the electrolyte; The battery also includes tabs, the tabs include tab adhesive, the tab adhesive has a melting point of 100℃~160℃; the battery also includes an aluminum-plastic film, the aluminum-plastic film includes a heat-sealing layer, the heat-sealing layer has a melting point of 100℃~150℃; The content of the fluoroethylene carbonate (FEC) is 5wt%~15wt%; the content of the sulfolane (SL) is 0~1wt%; and the mass ratio of the ethylene carbonate (EC) to the propylene carbonate (PC) is 2:1~1:2.

5. The content of 1,3-propanesulfonate lactone is 1wt%~4wt%, the content of 1-propene-1,3-sulfonate lactone is 0wt%~1wt%, the content of butyrylsulfonate lactone is 0.5wt%~2wt%, and the content of ethylene sulfate is 0.5wt%~1wt%.

2. The battery according to claim 1, characterized in that, The graphite is graphite with amorphous carbon coated on its surface.

3. The battery according to claim 1, characterized in that, The electrolyte further includes a second additive, which is selected from one or more of the following compounds: vinylene carbonate, vinyl sulfate, butene sulfite, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide. And / or, the electrolyte further includes a second solvent selected from at least one linear carbonate and linear carboxylic acid ester.

4. The battery according to claim 1, characterized in that, The electrolyte is composed of organic solvents, lithium salts, and additives.

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